Remove school day hours from schedule templates

The day progress bar no longer uses day start/end times (it uses block
durations instead), so the field is no longer needed.

Removed from: Admin UI, schedule store, schedule model/schemas/router,
session broadcast payload, dashboard snapshot, and startup migrations.
DB columns are left in place (harmless, no migration required).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/schemas/schedule.py

@@ -47,8 +47,6 @@ class ScheduleTemplateCreate(BaseModel):
     name: str
     child_id: int | None = None
     is_default: bool = False
-    day_start_time: time | None = None
-    day_end_time: time | None = None
     blocks: list[ScheduleBlockCreate] = []
 
 
@@ -56,8 +54,6 @@ class ScheduleTemplateUpdate(BaseModel):
     name: str | None = None
     child_id: int | None = None
     is_default: bool | None = None
-    day_start_time: time | None = None
-    day_end_time: time | None = None
 
 
 class ScheduleTemplateOut(BaseModel):
@@ -65,8 +61,6 @@ class ScheduleTemplateOut(BaseModel):
     name: str
     child_id: int | None
     is_default: bool
-    day_start_time: time | None
-    day_end_time: time | None
     blocks: list[ScheduleBlockOut] = []
 
     model_config = {"from_attributes": True}